Device and method for treatment of wounds with nitric oxide

ABSTRACT

Topical exposure of nitric oxide gas to wounds such as chronic non-healing wounds may be beneficial in promoting healing and preparing the wound bed for further treatment and recovery. Nitric oxide gas may be used to reduce the microbial infection, manage exudates secretion by reducing inflammation, upregulate expression of endogenous collagenase to locally debride the wound, and regulate the formation of collagen. High concentration of nitric oxide ranging from 160–400 ppm may be used without inducing toxicity in the healthy cells around a wound site. Exposure to the high concentration for a first treatment period reduces the microbial burden and inflammation, and increases collagenase expression to debride necrotic tissue at the wound site. After a first treatment period, a second treatment period at a lower concentration of nitric oxide, preferably ranging from 5–20 ppm may be used to restore the balance of nitric oxide and induce collagen expression aiding in the wound closure.

This application is a continuation in part of U.S. application Ser. No.10/944,479, filed Sep. 17, 2004, and U.S. application Ser. No.10/615,546, filed Jul. 8, 2003.

U.S. application Ser. No. 10/944,479 is a continuation of U.S.application Ser. No. 10/172,270, filed Jun. 14, 2002 and issued as U.S.Pat. No. 6,793,644, which in turn is a continuation of U.S. applicationSer. No. 09/749,022, filed on Dec. 26, 2000 and issued as U.S. Pat. No.6,432,077.

U.S. application Ser. No. 10/615,546 claims priority to U.S. ProvisionalApplication Nos. 60/431,876, filed Dec. 9, 2002, 60/409,400, filed Sep.10, 2002, and 60/394,690, filed Jul. 9, 2002.

The above patents and patent applications are incorporated by referenceas if set forth fully herein.

FIELD OF THE INVENTION

The field of the invention relates to devices and methods for treatingwounds and infections, and more specifically, the treatment of woundsand infections with nitric oxide.

BACKGROUND OF THE INVENTION

The treatment of infected surface or subsurface lesions in patients hastypically involved the topical or systemic administration ofanti-infective agents to a patient. Antibiotics are one such class ofanti-infective agents that are commonly used to treat an infectedabscess, lesion, wound, or the like. Unfortunately, an increasinglynumber of infective agents such as bacteria have become resistant toconventional antibiotic therapy. Indeed, the increased use ofantibiotics by the medical community has led to a commensurate increasein resistant strains of bacteria that do not respond to traditional oreven newly developed anti-bacterial agents.

For example, Staphylococci are known to be significant pathogens thatcause severe infections in humans, including endocarditis, pneumonia,sepsis and toxic shock. Methicillin resistant S. aureus (MRSA) is nowone of the most common causes of nosocomial infections worldwide,causing up to 89.5% of all staphylococci infection. Community outbreaksof MRSA have also become increasingly frequent. The main treatment forthese infections is the administration of glycopeptides (Vancomycin andTeicoplanin). MRSA have been reported for two decades, but emergence ofglycopeptide-resistance in S. aureus—namely glycopeptide intermediate(GISA) has been reported only since 1997.²² The glycopeptides are givenonly parenterally, and have many toxic side effects. The recentisolation of the first clinical Vancomycin-resistant strains (VRSA) froma patient in USA has heightened the importance and urgency of developingnew agents. Even when new anti-infective agents are developed, theseagents are extremely expensive and available only to a limited patientpopulation.

P. aeruginosa is another problematic pathogen that is difficult to treatbecause of its resistance to antibiotics. It is often acquired in thehospital and causes severe respiratory tract infections. P. aeruginosais also associated with high mortality in patients with cystic fibrosis,severe bums, and in AIDS patients who are immunosuppressed. The clinicalproblems associated with this pathogen are many, as it is notorious forits resistance to antibiotics due to the permeability barrier affordedby its outer membrane lipopolysaccharide (LPS). The tendency of P.aeruginosa to colonize surfaces in a biofilm phenotype makes the cellsimpervious to therapeutic concentrations of antibiotics.

Another problem with conventional anti-infective agents is that somepatients are allergic to the very compounds necessary to their treattheir infection. For these patients, only few drugs might be availableto treat the infection. If the patient is infected with a strain ofbacteria that does not respond well to substitute therapies, thepatient's life can be in danger.

A separate problem related to conventional treatment of surface orsubsurface infections is that the infective agent interferes with thecirculation of blood within the infected region. It is sometimes thecase that the infective agent causes constriction of the capillaries orother small blood vessels in the infected region which reducesbloodflow. When bloodflow is reduced, a lower level of anti-infectiveagent can be delivered to the infected region. In addition, theinfection can take a much longer time to heal when bloodflow isrestricted to the infected area. This increases the total amount of drugthat must be administered to the patient, thereby increasing the cost ofusing such drugs. Topical agents may sometimes be applied over theinfected region. However, topical anti-infective agents do not penetratedeep within the skin where a significant portion of the bacteria oftenreside. Topical treatments of anti-infective agents are often lesseffective at eliminating infection than systemic administration (i.e.,oral administration) of an anti-infective pharmaceutical.

In addition, despite recent advances in chronic wound care, many lowerextremity ulcers do not heal. Chronic ulcers of the lower extremitiesare a significant public health problem. Besides the large financialburden placed on the health care system for their treatment, they causea heavy toll in human suffering. As the population ages and with thecurrent obesity crisis in North America, venous, diabetic, and pressureulcers are likely to become ever more common. Approximately 4 million(1% of population) people in the United States develop chronic lower legulcers, the majority classified as diabetic or venous leg ulcers, andthis number can climb to 4%–5% in older (>80 years of age) patients.

Aside from infection, a variety of factors can potentially influencewound healing of chronic ulcers. These include excessive exudate,necrotic tissue, poor tissue handling, and impaired tissue perfusion, aswell as from clinical conditions such as advanced age, diabetes, andsteroid administration.

Exudate is a clear, straw colored liquid produced by the body inresponse to tissue damage. Although exudate is primarily water, it alsocontains cellular materials, antibodies, nutrients and oxygen. In theimmediate response to an injury, exudate is produced by the body toflush away any foreign materials from the site. It then is the carrierfor polymorphs and monocytes so that they may ingest bacteria and otherdebris. Exudate also enables the movement of these phagocytic cellswithin the wound to help clean it as well as enables the migration ofepithelial cells across the wound surface.

While exudate is an important component of wound healing, too much of itin response to chronic inflammation can worsen a wound as the enzymes inthe fluid can attack healthy tissues. This may exacerbate the failure ofthe wound to close as well as place additional psychological pressure onthe patient. Chronic wounds frequently have excessive exudate, usuallyassociated with a chronic infection and/or biofilm that has upregulatedthe inflammatory cells of the body. This may be a local response or mayinclude a systemic increase in inflammatory markers and circulatingcytokines.

Chronic wounds also lead to the formation of necrotic tissue, which inturn lead to growth of microbes. Debridement of necrotic tissue isdeemed as an important wound bed preparation for successful woundhealing. Sharp and surgical debridement rapidly remove necrotic tissueand reduce the bacterial burden, but also carry the greatest risk ofdamage to viable tissue and require high levels of technical skill.Chemical, mechanical and autolytic debridement are frequently regardedas safer options, although the risk to the patient of ongoing woundcomplications is greater.

Additionally, the collagenase family of Metalloproteinases (MMP's) are aclass of enzymes which are able to cleave native collagen intofragments. These fragments may then spontaneously denature into gelatin.Gelatin peptides are further cleaved by gelatinases such as MMP-2. Sincethe dry weight of skin is composed of 70–80% collagen, and sincenecrotic tissue is anchored to the wound bed by collagen fibers, enzymeswhich cleave collagen may be beneficial and assist in the debridement ofthis tissue. However, in chronic non-healing wounds, the levels andactivity of collagenases are insufficient for the removal of necrotictissue. Jung K, Knoll A G, Considerations for the use of Clostridialcollagenase in clinical practice. Clin Drug Invest 1998; 15:245–252.Also, wound fluid from diabetics, for example, may have decreased MMP-2activity. Furthermore, while exogenous application of collagenase hasbeen proposed, its application suffers from the drawback of not beingselective and risk the cleavage of collagen anchoring healthy cells inaddition to necrotic tissue.

In the 1980's, it was discovered by researchers that the endotheliumtissue of the human body produced nitric oxide (NO), and that NO is anendogenous vasodilator, namely, an agent that widens the internaldiameter of blood vessels. NO is most commonly known as an environmentalpollutant that is produced as a byproduct of combustion. At lowconcentrations such as less than 100 ppm, researchers have discoveredthat inhaled NO can be used to treat various pulmonary diseases inpatients. For example, NO has been investigated for the treatment ofpatients with increased airway resistance as a result of emphysema,chronic bronchitis, asthma, adult respiratory distress syndrome (ARDS),and chronic obstructive pulmonary disease (COPD).

While NO has shown promise with respect to certain medical applications,delivery methods and devices must cope with certain problems inherentwith gaseous NO delivery. First, exposure to high concentrations of NOmay be toxic, especially exposure to NO in concentrations over 1000 ppm.Even lower levels of NO, however, can be harmful if the time of exposureis relatively high. For example, the Occupational Safety and HealthAdministration (OSHA) has set exposure limits for NO in the workplace at25 ppm time-weighted averaged for eight (8) hours. It is extremelyimportant that any device or system for delivering NO include featuresthat prevent the leaking of NO into the surrounding environment. If thedevice is used within a closed space, such as a hospital room or athome, dangerously high levels of NO can build up in a short period oftime. One concern over NO toxicity is the binding of NO, when absorbedinto the circulation system such as through inhalation, to hemoglobinthat give rise to methemoglobin

Another problem with the delivery of NO is that NO rapidly oxidizes inthe presence of oxygen to form NO₂, which is highly toxic, even at lowlevels. If the delivery device contains a leak, unacceptably high levelsNO₂ of can develop. In addition, to the extent that NO oxidizes to formNO₂, there is less NO available for the desired therapeutic effect. Therate of oxidation of NO to NO₂ is dependent on numerous factors,including the concentration of NO, the concentration of O₂, and the timeavailable for reaction. Since NO will react with the oxygen in the airto convert to NO₂, it is desirable to have minimal contact between theNO gas and the outside environment.

Accordingly, there is a need for a device and method for the treatmentof surface and subsurface infections and wounds by the topicalapplication of NO. The device is preferably leak proof to the largestextent possible to avoid a dangerous build up of NO and NO₂concentrations. In addition, the device should deliver NO to theinfected region of the patient without allowing the introduction of airthat would otherwise react with NO to produce NO₂. The application of NOto the infected region preferably decreases the time required to healthe infected area by reducing pathogen levels. The device preferablyincludes a NO and NO₂ absorber or scrubber that will remove orchemically alter NO and NO₂ prior to discharge of the air from thedelivery device.

SUMMARY OF THE INVENTION

It has been discovered that NO will interfere with or kill the growth ofbacteria grown in vitro and has been investigated for its use as asterilizing agent. PCT International Application No. PCT/CA99/01123published Jun. 2, 2000, by one of the named inventors of the presentapplication, discloses a method and apparatus for the treatment ofrespiratory infections by NO inhalation.

Topical exposure of nitric oxide gas to wounds such as chronicnon-healing wounds may be beneficial in promoting healing of the woundand in preparing the wound bed for further treatment and recovery.Nitric oxide gas may be used, for example, to reduce the microbialinfection and burden on these wounds, manage exudate secretion byreducing inflammation, upregulate expression of endogenous collagenaseto locally debride the wound, and regulate the formation of collagen.

In a first aspect of the invention, a device for the topical delivery ofnitric oxide gas to an infected area of skin includes a source of nitricoxide gas, a bathing unit, a flow control valve, and a vacuum unit. Thebathing unit is in fluid communication with the source of nitric oxidegas and is adapted for surrounding the area of infected skin and forminga substantially air-tight seal with the skin surface. The flow controlvalve is positioned downstream of the source of nitric oxide andupstream of the bathing unit for controlling the amount of nitric oxidegas that is delivered to the bathing unit. The vacuum unit is positioneddownstream of the bathing unit for withdrawing gas from the bathingunit.

In a second aspect of the invention, the device according to the firstaspect of the invention includes a controller for controlling theoperation of the flow control valve and the vacuum unit.

In a third aspect of the invention, the device according to the firstaspect of the invention further includes a source of diluent gas and agas blender. The diluent gas and the nitric oxide gas are mixed by thegas blender. The device also includes a nitric oxide gas absorber unitthat is positioned upstream of the vacuum unit. The device also includesa controller for controlling the operation of the flow control valve andthe vacuum unit.

In a fourth aspect of the invention, a method of delivering an effectiveamount of nitric oxide to an infected area of skin includes the steps ofproviding a bathing unit around the infected area of skin, the bathingunit forming a substantially air-tight seal with the skin. Gascontaining nitric oxide is then transported to the bathing unit so as tobathe the infected area of skin with gaseous nitric oxide. Finally, atleast a portion of the nitric oxide gas is evacuated from the bathingunit.

In a fifth aspect of the invention a method of treating infected tissuewith topical nitric oxide exposure includes the steps of providing asource of nitric oxide containing gas and delivering the nitric oxidecontaining gas to a skin surface containing infected tissue so as tobathe the infected tissue with nitric oxide.

In a sixth aspect of the invention, a method of treating wounds withtopical nitric oxide exposure includes the steps of providing a sourceof nitric oxide containing gas and delivering the nitric oxidecontaining gas to the wound so as to bathe the wound with nitric oxide.Preferably, the treatment method includes continuous exposure of thewound to a sufficiently high concentration of nitric oxide gas for asufficient amount of time to kill or effect a 2–3 log₁₀ reduction in themicroorganism population at the wound site, without significant toxicityto the subject or the host cells of the treated subject. For example,the high concentration of nitric oxide gas may range from about 120 ppmto about 400 ppm, and more preferably at about 200 ppm to 250 ppm. Theamount of time for the exposure of nitric oxide may also range from 5hours to 96 hours, yet optimal exposure time and concentration can bedetermined based on the individual condition of the subject asprescribed by a physician. In another embodiment, the treatment methodmay also include a second treatment period, subsequent to the firsttreatment period with high concentration of nitric oxide gas, in whichthe wound is treated with a lower concentration of nitric oxide gas.Preferably, the lower concentration of nitric oxide gas ranges from 1ppm to 80 ppm, and more preferably ranges from 5 ppm to 20 ppm. Theexposure time for the second treatment period may also range from 5hours to 96 hours, depending on the individual condition of the treatedsubject. In another embodiment, the wound is exposed to 200 ppm ofnitric oxide gas for about 7–8 hours preferably during the night whilethe patient sleeps, and nitric oxide exposure may be withdrawn duringthe day time, or provided at a low concentration (e.g., 5 ppm to 20 ppm)for about 5–16 hours.

In a seventh aspect of the invention, a method of managing exudatesecretion in a wound with topical exposure of nitric oxide includes thesteps of removing excess exudate, dressing the wound with a gaspermeable dressing, providing a source of nitric oxide containing gas,and delivering the nitric oxide containing gas to the wound so as tobathe the wound with nitric oxide.

In an eighth aspect of the invention, a method of debriding a wound withtopical exposure of nitric oxide includes the steps of providing asource of nitric oxide containing gas, and delivering the nitric oxidecontaining gas to the wound so as to upregulate the expression ofendogenous enzymes such as collagenase and gelatinase by the host cellslocated locally at the wound site of the treated subject. Preferably,the treatment method includes exposure of the wound to a sufficientlyhigh concentration of nitric oxide gas for a sufficient amount of timeto upregulate expression of endogenous collagenase without significanttoxicity to the host cells of the treated subject. For example, the highconcentration of nitric oxide gas may range from 120 ppm to 400 ppm, andmore preferably at about 200 ppm–250 ppm. The amount of time for theexposure of nitric oxide may also range from 5 hours to 72 hours, yetoptimal exposure time and concentration can be determined based on theindividual condition of the subject as prescribed by a physician.Preferably, the expression of collagenase in the host cells may bemonitored by taking biopsies and analyzing the expression of collagenaseMRNA or protein through a various of techniques available in the art,such as Northern blot, RT-PCR, quantitative RT-PCR, immunostaining,immunoprecipitation, or ELISA. Additionally, after the treatment periodwith the high concentration of nitric oxide gas, the wound may also beexposed to a lower concentration for a second treatment period so as toreduce collagenase expression and increase collagen expression.

In a ninth aspect of the invention, a method for wound bed preparationwith topical nitric oxide exposure includes the steps of providing asource of nitric oxide gas and delivering the nitric oxide containinggas to the wound.

In a tenth aspect of the invention, a method of reducing scarring in thehealing process of a wound with topical nitric oxide exposure includesproviding a source of nitric oxide gas, exposing the wound to a highconcentration of exogenous nitric oxide gas for a treatment periodwithout inducing toxicity to the subject or to healthy cells surroundingthe wound, exposing the wound to a decreased concentration of exogenousnitric oxide gas for a second treatment period sufficient to increasethe expression of collagen mRNA; and exposing the wound to a thirdconcentration of exogenous nitric oxide gas for a third treatmentperiod, wherein the third concentration is between the highconcentration and the decreased concentration. The high concentrationpreferably ranges from about 200 ppm to 400 ppm, the decreasedconcentration preferably ranges from about 5–20 ppm, and the thirdconcentration ranges from about 20 ppm to 200 ppm. Also, the firsttreatment period is preferably at least seven hours in a day, and thesecond and third treatment periods, each preferably ranges from about5–12 hours in a day. The three step treatment may also be provided formultiple days, and preferably for at least 3–14 days.

It is an object of the invention to provide a delivery device for thetopical delivery of a NO-containing gas to any exposed wounds on theskin surface or subsurface, or any exposed surface of the body such asthe eye, or any exposed internal organs of the body. It is a furtherobject of the device to prevent the NO-containing gas from leaking fromthe delivery device. The method of delivering an effective amount ofnitric oxide gas to the infected or wounded area kills bacteria andother pathogens and promotes the healing process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic representation of the NO delivery deviceaccording to one aspect of the invention.

FIG. 2 illustrates a bathing unit surrounding the foot of a patient.

FIG. 3 illustrates a bathing unit surrounding the hand of a patient.

FIG. 4 illustrates a bathing unit including an agitator located therein.

FIG. 5 shows a specialized gaseous nitric oxide (gNO) incubation chamberdesigned to conduct in vitro studies on the effects of gNO exposure onmammalian cell cultures as well as microbial cells under optimal growthconditions.

FIG. 6 depicts a S. aureus dosage curve for exposure to gaseous NO (gNO)with bacteria grown on solid media. Relative percentages of growth of S.aureus colony forming units (cfu) at 50, 80, 120 and 160 parts permillion (ppm) of nitric oxide compared with growth of S. aureus cfu inmedical air (100%) are shown.

FIG. 7 depicts a Pseudomonas aeruginosa dosage curve for exposure to NOgas with bacteria grown on solid media. Relative percentages of growthof P. aeruginosa colony forming units (cfu) at 50, 80, 120 and 160 partsper million (ppm) of nitric oxide compared with growth of P. aeruginosacfu in medical air (100%) are shown.

FIG. 8 a–8 m depict the bacteriocidal effect of 200 ppm gNO on a varietyof microbes.

FIG. 9 illustrates wound bacterial content following topical applicationof 200 ppm gNO in a full thickness infected wound model in rabbits.

FIG. 10 shows wound bacterial content following topical application of400 ppm gNO in a full thickness infected wound model in rabbits.

FIG. 11 shows rabbit blood serum NOx (NO₂ & NO₃) levels followingtopical application of 400 ppm gNO.

FIG. 12 illustrates rabbit blood methemoglobin levels following topicalapplication of 400 ppm gNO on a full thickness infected wound model.

FIG. 13 illustrates histology analysis of full thickness infected woundexposed to 200 ppm gNO for 24 hours.

FIG. 14 shows MRNA expression for collagen and collagenase followingexposure to 200 ppm gNO for 24 hours and 48 hours.

FIG. 15 illustrates the morphology of fibroblast cells exposed insidegNO chamber to less than 200 ppm NO versus control group insideconventional tissue culture incubator.

FIG. 16 illustrates increase in fibroblast cell proliferation followingexposure to 200 ppm of NO in comparison with control.

FIG. 17 illustrates cell attachment capacity of human fibroblastsfollowing exposure to160 ppm of gNO.

FIG. 18 shows the results of fibroblasts grown in a 3D matrix andexposed to 200 ppm NO for 8 hours per day for 3 days compared withcontrol cells in air or conventional incubator.

FIG. 19 shows the amount of proliferation of fibroblasts grown in a 3Dmatrix and exposed to 200 ppm NO for 8 hours per day for 3 days comparedwith control cells in air or conventional incubator.

FIG. 20 shows the amount of tube formation in human endothelial cellsgrown in matrigel and exposed to air (top panels) or 200 ppm NO (bottompanels) for 24 hours. Left panels at 8 hours of exposure. Right panelsat 24 hours of exposure.

FIG. 21 shows an increased collagen MRNA expression in fibroblastexposed to 5 ppm of NO.

FIG. 22 shows various photographs of a human non-healing leg ulcers atvarious stages of treatment with nitric oxide gas.

FIG. 23 shows the reduction in wound size in the human non-healing ulcerof FIG. 23 following nitric oxide gas treatment. Significant decrease inarea was observed following 3 and 14 days of gNO application to thewound (*p=0.019 vs. day 0; **p=0.014 vs. day 3). Wound status did notdeteriorate after removal of treatment (arrow, day 14). Wound wascompletely healed following 26 weeks (186 days; ***p<0.01 vs. day 3).Values are means and standard deviations.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, a NO delivery device 2 is shown connected to apatient 4. In its most general sense, the NO delivery device 2 includesa bathing unit 6 that is fluidically connected to a NO gas source 8, aflow control valve 22, and a vacuum unit 10. FIG. 1 illustrates onepreferred embodiment of the invention.

In FIG. 1, the NO gas source 8 is a pressurized cylinder containing NOgas. While the use of a pressurized cylinder is the preferred method ofstoring the NO-containing gas source 8, other storage and deliverymeans, such as a dedicated feed line (wall supply) can also be used.Typically, the NO gas source 8 is a mixture of N₂ and NO. While N₂ istypically used to dilute the concentration of NO within the pressurizedcylinder, any inert gas can also be used. When the NO gas source 8 isstored in a pressurized cylinder, it is preferable that theconcentration of NO in the pressurized cylinder fall within the range ofabout 800 ppm to about 2500 ppm. Commercial nitric oxide manufacturerstypically produce nitric oxide mixtures for medical use at around the1000 ppm range. Extremely high concentrations of NO are undesirablebecause accidental leakage of NO gas is more hazardous, and high partialpressures of NO tends to cause the spontaneous degradation of NO intonitrogen. Pressurized cylinders containing low concentrations of NO(e.g., less than 100 ppm NO) can also be used in accordance with thedevice and method disclosed herein. Of course, the lower theconcentration of NO used, the more often the pressurized cylinders willneed replacement.

FIG. 1 also shows source of diluent gas 14 as part of the NO deliverydevice 2 that is used to dilute the concentration of NO. The source ofdiluent gas 14 can contain N₂, O₂, Air, an inert gas, or a mixture ofthese gases. It is preferable to use a gas such as N₂ or an inert gas todilute the NO concentration since these gases will not oxidize the NOinto NO₂ as would O₂ or air. The source of diluent gas 14 is shown asbeing stored within a pressurized cylinder. While the use of apressurized cylinder is shown in FIG. 1 as the means for storing thesource of diluent gas 14, other storage and delivery means, such as adedicated feed line (wall supply) can also be used.

The NO gas from the NO gas source 8 and the diluent gas from the diluentgas source 14 preferably pass through pressure regulators 16 to reducethe pressure of gas that is admitted to the NO delivery device 2. Therespective gas streams pass via tubing 18 to an optional gas blender 20.The gas blender 20 mixes the NO gas and the diluent gas to produce aNO-containing gas that has a reduced concentration of NO. Preferably,the NO-containing gas that is output from the gas blender 20 has aconcentration that is less than about 400 ppm and more preferably about200 ppm. Depending on the concentration needed for the specificapplication, the concentration of NO-containing gas that is output fromthe gas blender 20 can also be regulated to less than about 100 ppm orless than about 40 ppm, if desired.

The NO-containing gas that is output from the gas blender 20 travels viatubing 18 to a flow control valve 22. The flow control valve 22 caninclude, for example, a proportional control valve that opens (orcloses) in a progressively increasing (or decreasing if closing) manner.As another example, the flow control valve 22 can include a mass flowcontroller. The flow control valve 22 controls the flow rate of theNO-containing gas that is input to the bathing unit 6. The NO-containinggas leaves the flow control valve 22 via flexible tubing 24. Theflexible tubing 24 attaches to an inlet 26 in the bathing unit 6. Theinlet 26 might include an optional one way valve 64 (see FIG. 3) thatprevents the backflow of gas into the tubing 24.

Still referring to FIG. 1, the bathing unit 6 is shown sealed againstthe skin surface of a patient 4. The infected area 30 which can be anabscess, lesion, wound, or the like, is enclosed by the bathing unit 6.The bathing unit 6 preferably includes a seal portion 32 that forms asubstantially air-tight seal with the skin of the patient 4, or anyother exposed surface of the body (e.g., eye) or exposed internal organsdesired to be treated. Substantially air-tight is meant to indicate thatthe NO-containing gas does not leak out of the bathing unit 6 insignificant amounts (i.e., no more than about 5% of the NO-containinggas delivered to the bathing unit 6). The seal portion 32 may comprisean inflatable seal 61, such as that shown in FIGS. 2 and 3, oralternatively the seal portion 32 may comprise a flexible skirt or thelike that confirms to the surface of the patient 4. The seal portion 32also might include an adhesive portion that adheres to the skin surfaceof a patient 4. In other envisioned embodiments, the sealing portion 32may merely comprise the interface of the bathing unit 6 with the surfaceof the patient's 4 skin.

The bathing unit 6 can be made of a virtually limitless number of shapesand materials depending on its intended use. The bathing unit 6 might beformed as a rigid structure, such as that shown in FIG. 1, that isplaced over the infected area 30. Alternatively, the bathing unit 6 canbe formed of a flexible, bag-like material that is inflatable over theinfected area 30. FIG. 2 shows such a structure in the shape of a bootthat is placed over the patient's 4 foot. FIG. 3 shows anotherinflatable bathing unit 6 that is formed in the shape of a mitten orglove that is worn over the patient's 4 hand.

In one preferred embodiment of the invention, the bathing unit 6includes an NO sensor 34 that measures the concentration of NO gaswithin the bathing unit 6. The NO sensor 34 preferably reports thisinformation to a controller 36 via signal line 38. An optional NO₂sensor 40 can also be included within the bathing unit 6. The NO₂ sensor40 preferably reports the concentration of NO₂ to the controller 36 viasignal line 42. The sensors 40, 42 can be a chemilluminesense-type,electrochemical cell-type, or spectrophotometric-type sensor.

The bathing unit 6 also includes an outlet 44 that is used to remove gasfrom the bathing unit 6. The outlet 44 is preferably located away fromthe gas inlet 26 such that NO gas does not quickly enter and exit thebathing unit 6. Preferably, the inlet 26 and outlet 44 are located inareas of the bathing unit 6 such that the NO gas has a relatively longresidence time. Flexible tubing 46 is connected to the outlet 44 andprovides a conduit for the removal of gases from the bathing unit 6.

In one preferred embodiment of the invention, the flexible tubing 46 isin fluid communication with an absorber unit 48. The absorber unit 48preferably absorbs or strips NO from the gas stream that is exhaustedfrom the bathing unit 6. It is also preferable for the absorber unit 48to also absorb or strip NO₂ from the gas stream that is exhausted fromthe bathing unit 6. Since these gases are toxic at high levels, it ispreferable that these components are removed from the delivery device 2prior to the gas being vented to the atmosphere. In addition, thesegases can react with the internal components of the vacuum unit 10 andinterfere with the operation of the delivery device 2.

The now clean gas travels from the absorbing unit 48 to the vacuum unit10 via tubing 50. The vacuum unit 10 provides a negative pressure withinthe tubing 50 so as to extract gases from the bathing unit 6. The vacuumunit 10 is preferably controllable with respect to the level of vacuumor suction supplied to the tubing 50 and bathing unit 6. In this regard,in conjunction with the flow control valve 22, the amount of NO gaswithin the bathing unit 6 can be regulated. Preferably, the vacuum unit10 is coupled with the controller 36 via a signal line 52. Thecontroller 36, as discussed below, preferably controls the level ofoutput of the vacuum unit 10. The gas then passes from the vacuum unit10 to a vent 54 that is open to the atmosphere.

It should be understood that the absorbing unit 48 is an optionalcomponent of the delivery device 2. The gas laden with NO and NO₂ doesnot have to be removed from the gas stream if there is no concern withlocal levels of NO and NO₂. For example, the gas can be exhausted to theoutside environment where high concentrations of NO and NO₂ will notdevelop. Alternatively, a recirculation system (not shown) might be usedto recycle NO with the bathing unit 6.

Still referring to FIG. 1, the delivery device 2 preferably includes acontroller 36 that is capable of controlling the flow control valve 22and the vacuum unit 10. The controller 36 is preferably amicroprocessor-based controller 36 that is connected to an input device56. The input device 56 is used by an operator to adjust variousparameters of the delivery device such as NO concentration, residence orexposure time of NO, pressure within the bathing unit 6, etc. Anoptional display 58 can also be connected with the controller 36 todisplay measured parameters and settings such as the set-point NOconcentration, the concentration of NO within the bathing unit 6, theconcentration of NO₂ within the bathing unit 6, the flow rate of gasinto the bathing unit 6, the flow rate of gas out of the bathing unit 6,the total time of delivery, and the like.

The controller 36 preferably receives signals from sensors 34, 40regarding gas concentrations if such sensors 34, 40 are present withinthe delivery device 2. Signal lines 60, 52 are connected to the flowcontrol valve 22 and vacuum unit 10 respectively for the delivery andreceipt of control signals.

In another embodiment of the invention, the controller 36 is eliminatedentirely. In this regard, the flow rate of the gas into the bathing unit6 and the flow rate of the gas out of the bathing unit 6 are pre-set oradjusted manually. For example, an operator can set a vacuum output thatis substantially equal to the flow rate of the gas delivered to thebathing unit 6 via the flow control valve 22. In this manner, NO gaswill be able to bathe the infected area 30 without any build-up orleaking of NO or NO₂ gas from the delivery device 2.

FIG. 2 illustrates a bathing unit 6 in the shape of a boot that is usedto treat an infected area 30 located on the leg of the patient 4. Thebathing unit 6 includes an inflatable seal 61 that surrounds the legregion to make a substantially air-tight seal with the skin of thepatient 4. This embodiment shows a nozzle 62 that is affixed near theinlet 26 of the bathing unit 6. The nozzle 62 directs a jet of NO gasonto the infected area 30. The jet of gaseous NO aids in penetrating theinfected area 30 with NO to kill or inhibit the growth of pathogens.FIG. 3 shows another embodiment of the bathing unit 6 in the shape of amitten or glove. The bathing unit 6 is also inflatable and contains aninflatable seal 61 that forms a substantially air-tight seal around theskin of the patient 4. FIG. 3 also shows an optional one way valve 64located in the inlet 26. As seen in FIGS. 3 and 4, the inlet 26 andoutlet 44 are located away from one another, and preferably on opposingsides of the treated area such that freshly delivered NO gas is notprematurely withdrawn from the bathing unit 6.

For treatment of an infected area 30, the bathing unit 6 is placed overthe infected area 30. An air-tight seal is then formed between the skinof the patient 4 and the bathing unit 6. If the bathing unit 6 has aninflatable construction, the bathing unit 6 must be inflated with gas.Preferably, the bathing unit 6 is initially inflated only with thediluent gas to prevent the leaking of NO and NO₂ from the device 2. Oncean adequate air-tight seal has been established, the operator of thedevice initiates the flow of NO from the NO gas source 8 to the bathingunit 6. As described above, this may be accomplished manually or via thecontroller 36.

Once the bathing unit 6 has started to fill with NO gas, the vacuum unit10 is turned on and adjusted to the appropriate output level. For aninflatable bathing unit 6, the output level (i.e., flow rate) of thevacuum unit 10 should be less than or equal to the flow rate of NO gasentering the bathing unit 6 to avoid deflating the bathing unit 6. Inembodiments of the device where the bathing unit 6 is rigid, the vacuumunit 10 can be set to create a partial vacuum within the bathing unit 4.In this regard, the partial vacuum helps to form the air-tight sealbetween the skin of the patient 4 and the bathing unit 6. Of course, thevacuum unit 10 can also be set to withdraw gas at a substantially equalrate as the gas is delivered to the bathing unit 6. An effective amountof NO is delivered to the bathing unit 6 to kill pathogens and/or reducethe growth rate of the pathogens in the infected area 30. Pathogensinclude bacteria, viruses, and fungi.

FIG. 4 shows another embodiment of the invention in which the bathingunit 6 includes an agitator 66 that is used to create turbulentconditions inside the bathing unit 6. The agitator 66 preferably is afan-type of mechanism but can include other means of creating turbulentconditions within the bathing unit 6. The agitator 66 aids in refreshingthe infected area 30 with a fresh supply of NO gas.

Examples of Nitric Oxide Applications

In chronic non-healing wound such as in patients suffering from diabeticlesions, a variety of factors can potentially influence wound healing,including infections, excessive exudate, necrotic tissue, poor tissuehandling, and impaired tissue perfusion. Nitric oxide gas can be used toreduced the infection or microbial burden on the wound. While theexamples discussed below are applications of nitric oxide to the skin,nitric oxide can also be topically applied to other surfaces of the bodysuch as the eye, or any other exposed surface such as muscle, ligaments,tendons, and internal organs of the body that may be exposed, forexample, due to cut, tear, or wound.

To study the effects of gaseous nitric oxide on potential pathogens, acustom gas exposure incubator was designed and validated fortemperature, humidity, and gas concentrations, providing an environmentthat matches that of a microbiologic incubator, while enablingcontrolled exposure of precise concentrations of the gas. FIG. 5 shows aspecialized gaseous nitric oxide (gNO) incubation chamber designed toconduct in vitro studies on the effects of gNO exposure on mammaliancell cultures as well as microbial cells under optimal growthconditions. The gNO chamber allowed control and adjustment of followingfactors in all in vitro studies: gNO dose, total air flow, NO₂ levels,O₂ levels, CO₂ levels, temperature, and humidity.

For the initial pilot studies, two strains of bacterial pathogen wereselected based on two proposed clinical applications of gNO forrespiratory infections and topical application. P. aeruginosa isassociated primarily with pulmonary disease, but may also be associatedwith skin infection such as in severe bums. S. aureus is associated withsurface wound infections. Both of these mcro-organisms were chosen forthe pilot study.

The first step in the process of evaluating the direct effect of gNO onbacteria was to design a simple study to determine what dose, if any,would be an approximate lethal concentration level for microbes. Once anoptimal dose was estimated, then a timing study would be conducted. Forthese initial studies, highly dense inoculums of P. aeruginosa and S.aureus suspensions (10⁸ cfu/ml) were plated onto agar plates. Theseplates were then exposed to various concentrations of gNO in theexposure device in order to evaluate the effect on colony growth.

FIGS. 6 and 7 demonstrate that levels of gNO greater than 120 ppmreduced the colony formation of the bacteria by greater than 90%.Further studies indicated that the time required to achieve this affectoccurred between 8–12 hours. These results confirm that gNO has aninhibitory effect on P. aeruginosa and S. aureus growth. Additionally,the data provide preliminary evidence that there is a time and doserelationship trend, with the amount of bacteriocidal activity increasingwith increased time of exposure and concentration of gNO. That is, asthe concentration of gNO increases, the number of colonies growing onthe plates decreases.

Although there was a downward bacteriocidal trend towards 5–10% survivalwith increasing gNO to 120 ppm, none of the initial data showed a 100%bacteriocidal effect. Some bacteria may have survived because thematerials and chemicals in the agar may have reacted with the gNO andbuffered the effect. Of significance, was the observation that bacterialcolonies remained the same in size and number after being transferred toa conventional incubator for 24 hours whereas controls increased innumber and size to the degree that they could not be counted. Thisstrongly suggested that gNO exposure prevented the growth of thebacteria, and may have killed the bacteria at some point during the gNOexposure. Accordingly, subsequent studies were designed to further studythe bacteriocidal effects of gNO.

Following the dose and time ranging studies, a series of experimentswere performed to determine the time required to effectively induce abacteriocidal effect with 200 parts per million of gNO, a concentrationjust above the dose used in the dose-ranging study, on a representativecollection of drug resistant gram-positive and gram-negative strains ofbacteria associated with clinical infection. A successful bacteriocidaleffect was defined as a decrease in bacteria greater than 3 log₁₀cfu/ml. Further, C. albicans, Methicillin Resistant S. aureus (MRSA), aparticularly resistant strain of P. aeruginosa from a cystic fibrosispatient, Group B Streptococcus, and M. smegmatis were also included tosee if yeast, multi-drug resistant strains of bacteria, andactinomycetes have a similar response. The drug-resistant bacteriarepresent a variety of pathogens that contribute to both respiratory andwound infections.

For these experiments, saline was selected as a suspension media becauseit would not mask the direct effect of gNO as a bacteriocidal, whereasfully supplemented growth medium might introduce external variables(e.g., buffer or react with gNO). Other media might also providemetabolites and replenish nutrients that produce enzymes that protectbacteria from oxidative and nitrosative damage, thereby masking theeffect of gNO. Furthermore, it has been suggested that a salineenvironment more realistically represents the hostile host environmentto which bacteria are typically exposed in vivo. In saline, the colonieswere static but remained viable. This is similar to the approach ofWebert and Jean's use of animal models. Webert K E, et al (2000),Effects of inhaled nitric oxide in a rat model of Pseudomonas aeruginosapneumonia, Crit Care Med, 28(7):2397–2405 and Jean D, et al., (2002)Beneficial effects of nitric oxide inhalation on pulmonary bacterialclearance, Critical Care Medicine. 30(2):442–7.

FIG. 8 shows the results of these experiments with the line plotted bysquare-shaped points representing survival curves of the controlexposure microorganisms and the line plotted in triangle-shaped pointsrepresenting the survival curves of the NO exposed microorganisms. Thesestudies showed that gNO at 200 ppm had a completely bacteriocidal effecton all microorganisms tested. Without exception, every bacteriachallenged with 200 ppm gNO had at least a three log₁₀ reduction incfu/ml and every test resulted in a complete and total cell death of allbacteria. These results were also characterized by a period of latencywhen it appeared that the bacteria were unaffected by gNO exposure(Table 1). The latent period was then followed by an abrupt death of allcells. Gram negative and gram positive bacteria, antibiotic resistantbacterial strains, yeast and mycobacteria were all susceptible to 200ppm gNO. Of importance, is the observation that the two drug resistantbacteria strains were also susceptible. Accordingly, these results showthat gNO directly exhibits a non-specific lethal effect on a variety ofpotentially pathogenic microorganisms.

The study also indicates a significant difference in the lag period formycobacteria compared to all other organisms. The lag period suggeststhat mycobacteria may have a mechanism that protects the cell from thecytotoxicity of gNO for a longer period than other bacteria. Applicantsbelieve that there is a dose-time dependent gNO threshold reached withinthe cell at which point rapid cell death occurs. It is possible thatthis threshold occurs when the normal NO detoxification pathways of thebacteria are overwhelmed. These studies indicate and confirm thatsupraphysiologic levels of NO (provided exogenously, for example, viadelivery of 120 ppm to 400 ppm exogenous NO) may be bacteriocidal onrepresentative strains of drug resistant bacteria and the effect appearsto be abrupt, lethal and non-specific on these bacteria.

TABLE 1 Gram Latent −2.5 Log₁₀ LD₁₀₀ Bacteria staining Period* (hrs)(hrs) (Hrs) S. aureus (ATCC) Positive 3 3.3 4 P. aeruginosa (ATCC)Negative 1 2.1 3 MRSA Positive 3 4.2 5 Serracia sp. Negative 4 4.9 6 S.aureus (Clinical) Positive 3 3.7 4 Klebsiella sp. #1 Negative 3 3.5 6Klebsiella sp. #2 Negative 2 4.1 5 Klebsiella sp. #3 Negative 3 5.1 6 S.maltophilia Negative 2 2.8 4 Enterobacter sp. Negative 4 5.3 6Acinetobacter sp. Negative 4 5 6 E. coli Negative 3 4.2 5 Group BStreptococci Positive 1 1.5 2 Average N/A 2.77 3.82 4.77 SD N/A 1.011.17 1.30 Mycobacterium Positive 7 9.2 10

To achieve a lethal effect over a broad range of microbes, 200 ppm ofnitric oxide gas is preferably exposed to the wound site for at least 7hours continuously such as when the patient is asleep at night. Shortertimes may be used with higher concentration such as 400 ppm. Longertreatment options may also be provided that span days. Depending on thesubject, periods of breaks in between treatment may also be arranged.

In vivo studies in animal models have further shown the beneficialeffects of nitric oxide gas. In an animal model, full-thicknesscutaneous wounds (Set A: four rabbits with eight 8.0 mm punch biopsies &Set B: 4 rabbits with two 50×15 mm wounds) were made on each side ofdorsal midline and infected with equal volume of Staphylococcus aureussuspension on day zero. On day one, treated groups in A and B wererespectively exposed to 200 and 400 ppm gNO for total of three days. SetA was exposed for two 4-hour sessions, interrupted by 1-hour of rest,inside a specialized restraining exposure chamber. A 24-hour continuousdelivery model was used for animals in Set B by design of a specializedwound patch. Control groups were only exposed to medical grade air withcorresponding flow rate. Four random sample punch biopsies (8.0 mm) werecollected on post wounding days 3 and analyzed for bacterial content.Another four punch biopsies from both wound and normal skin tissue werecollected for fibroblast viability analysis and toxic effects of gNO.

FIG. 9 reveals data from the animal study on bacterial content of thewounds exposed to 200 ppm gNO continuously for 72 hours when compared tocontrol group only exposed to medical air. A significant bacterialreduction is observed in treated wounds. Rabbits appeared comfortableand at ease during the therapy and no toxic effect or damage wereobserved in the skin of treated animals when compared to the control.NO₂ did not exceed safety limits, at any point of the study, set byOccupational Safety and Health Administration (<4.3±0.3 ppm). FIG. 10shows similar set of data as seen in FIG. 9, but where animal woundswere exposed to 400 ppm of gNO therapy. On average well over 10 folddrop (p<0.05) in bacterial content is observed in comparison betweencontrol and treated groups.

FIG. 11 demonstrates that nitrogen oxides levels (NO₂ and NO₃), one ofend products of nitric oxide metabolism, measured in blood serumcollected from the animals following exposure to 200 ppm gNOintermittently for 6 days. None of the samples show an increased levelof NOx due to exposure to gNO indicating the fact that exposing fullthickness wounds (8 at 8.0 mm in diameter) will not increase the nitricoxide level in animal's circulation system.

FIG. 12 indicates the level of methemoglobin (MetHb) in animal's bloodfollowing 6 day intermittent exposure to 200 ppm gNO. Animals in thetreated group did not show an increase level of MetHB in comparison withthe control group exposed to air. This further supports the datapresented in FIG. 11 to the fact that topical application of gNO on openwounds did not contribute to an increase level of nitric oxide in thecirculation and that the topical application of an open wound to about200 ppm poses no significant toxicity concerns over the formation ofmethemoglobin.

FIG. 13 presents histological analysis of tissue blocks prepared onwound punch biopsies from animals in treated and control groups. Samplesfrom the control group show more advanced neutrophil infiltration and soa higher degree of inflammatory reaction. A lower level of neutrophilconcentration is seen in wounds treated with gNO. Wounds treated withgNO also show a layer of scab closing on the wound, but control woundsremain open for longer period of time. Overall, a healthier healingprocess is observed in the wounds treated with gNO. No toxic effects(cellular debris due to apoptosis) can be seen in gNO treated group.

While the inflammatory response is integral to wound healing, anaberrant inflammatory response is believed to be one causal factor inchronic wounds and excess exudate. NO inhibits platelet aggregation,assists in maintaining vascular tone, and inhibits mast celldegranulation. Delledonne M, et al., (2003) The functions of nitricoxide-mediated signaling and changes in gene expression during thehypersensitive response, Antioxid Redox Signal, 5:33–41. and Hickey MJ., (2001), Role of inducible nitric oxide synthase in the regulation ofleukocyte recruitment, Clin Sci (Lond), 100:1–12 NO producedconstitutively by endothelial cells has been shown to have an on-goinganti-inflammatory effect. Id. This may in part be due to its effect onplatelet aggregation. iNOS is upregulated during the inflammatoryresponse. Studies have shown that iNOS derived NO may also haveanti-inflammatory characteristics. Id. Collectively, by maintainingvascular tone, promoting angiogenesis, moderating inflammation andinhibiting mast cell degranulation, NO can be viewed as an importantmolecule for exudate management. Accordingly, exogenously applied nitricoxide may duplicate and supplement the actions of endogenous nitricoxide to reduce the local inflammatory response as well as down regulatethe message that the systemic inflammatory response system had beenreceiving to increase the sending of inflammatory cells. This eventuallymay lead to a healthy level of exudate production.

FIG. 14 shows that expression of collagenase MRNA is increased as theexposure time to high concentration of gNO (at 200 ppm) increases. Thissuggests that high concentration of nitric oxide upregulate collagenasethat may lead to the enzymatic cleavage of collagen. An independentstudy by Witte et al (2002) found that MMP-2 activity was alsoupregulated by NO donors. Witte M B, et al, (2002) Nitric oxide enhancesinvestigational wound healing in diabetes, Br J Surg., 89:1594–601.Thus, Applicants believe that NO may upregulate expression of bothcollagenase (MMP-1) and gelatinase (MMP-2), which may be important inkeeping the wound clean from necrotic tissue while not prolonging theinflammatory phase.

Rather than applying exogenous collagenase for enzymatic debridement ofnecrotic tissue, exposing a wound with necrotic tissue to exogenous NOgas to upregulate endogenous collagenase may be more beneficial. Whenendogenous collagenase is released by the cell, it automaticallyreleases TIMP's (tissue inhibitor of metalloproteinase). This ensuresthat the matrix degradation is coordinated and allows the establishmentof sharp geographical boundaries of collagenolytic activity and theprotection of areas of connective tissue from the activity of theenzyme. In contrast, use of exogenous collagenase material to debride awound confers no protection to specific areas of the wound as it isactive on every cell that comes in contact with it whether or not theeffect is desired. The ability of nitric oxide to debride a wound isfurther supported by the possible inhibition of collagen expression dueto high concentration of exogenous nitric oxide applied to the wound, asseen in FIG. 14 (left panel).

Preferably, after the exposure of the wound to high concentration ofnitric oxide gas for a first treatment period (e.g., 5–8 hours per day),the necrotic tissue may be mechanically removed easily and theconcentration of nitric oxide gas can be decreased for a secondtreatment period. The low concentration of nitric oxide gas (e.g., at5–20 ppm) delivered for the second treatment period may upregulate theexpression of collagen mRNA leading to synthesis of new collagen to aidin the closure of the wound. For example, FIG. 22 shows an increasedcollagen MRNA expression in fibroblast exposed to 5 ppm of NO. Thesecond treatment period may be for a period 7–16 hours per day. Further,the treatment with high and low concentration of nitric oxide gas can berepeated for several days.

For chronic non-healing ulcers on the skin, it is also possible to graftnatural skin tissue or synthetically produced skin tissue onto the ulcerafter the wound has been prepared. Wound bed preparation may include thereduction of microbial load, debridement, and the management of exudate.

It is believed that the body's natural response to injury is to increasethe amount of nitric oxide in order to reduce bacterial count at theinjury site, help remove dead cells and then promote healing. Themessage sent by the injury site has more than just the cells at theinjury site producing nitric oxide and this circulates NO around thebody in the blood stream. After a few days of this preparation forhealing, the body decreases the nitric oxide it produces to a new levelthat will promote healing. If a wound fails to heal or becomes infected,the body maintains the circulating nitric oxide at a high level and thewound is then caught with a concentration of nitric oxide that mayprevent it from healing. It becomes the “Catch 22” of wound healing.Bathing the injury site to high concentration of nitric oxide gas (e.g.,120 ppm to 400 ppm) sends a message to the body that there is enoughnitric oxide at the injury site and therefore the body can shut down theextra production by other cells. This enables the local site to healwhile it receives the appropriate supraphysiological concentration ofnitric oxide gas to inhibit microbial growth.

Additional Safety Studies

In addition to the above study showing no toxicity of in vivo exposureof 200 ppm of nitric oxide gas in an animal model for an open wound,studies to confirm the viability of normal host cells exposed to gNOwere performed on fibroblasts, endothelial cells, keratinocytes,alveolar epithelial cells, macrophages, and monocytes, in both flatplate and 3-D growth models for some studies. These experiments lookedat viability, proliferation, migration, attachment, expression and tubeformation in the appropriate models.

Fibroblast cells obtained from adult patients undergoing electivereconstructive surgery were cultured in Dulbeco's Modified Eagle'sMedium (DMEM), supplemented with 10% fetal bovine serum (FBS) andantibiotic-antimycotic preparation and divided into ten 25 cm² ventedculture flasks (COSTAR). Four of these flasks (treated group) wereexposed to 20 or 200 ppm humidified gNO inside a specialized NOincubation chamber at 37° C. for 24 and 48 hours. The NO exposurechamber was validated prior to the study to eliminate extraneousvariables and ensure optimal conditions for fibroblast cell growth.Another four flasks (control group) were placed inside conventionalculture incubator and exposed only to ambient humidified air at 37° C.Two flasks were separately harvested and counted as the number of cellsat zero time. Following the treatment, fibroblast cells were harvestedand evaluated for morphology, cell count, capacity to proliferate andmedium pH. The results from these experiments show that exposure toaround 200 ppm of gNO did not have harmful effects on the fibroblast.

FIG. 15 shows morphology of fibroblast cells from the viability study,where cultured human fibroblast cells were exposed to various gNOconcentrations less than 200 ppm continuously for 48 hours.Morphological appearance and attachment capacity of control and treateddermal fibroblasts cells following 48 hours period were quitecomparable. Cells under gNO appeared healthy and attached to the cultureplates. No toxic effect due to exposure to gNO was observed.

FIG. 16 shows that, in addition to a lack of toxicity to fibroblastcells, exposure to 200 ppm NO may also have positive effect ofincreasing proliferation of fibroblast cells that may further aid in thewound healing process.

FIG. 17 shows results from cell attachment capacity from the fibroblastcells exposed to 160 ppm of gNO. Capability of cells to reattach to theculture plates within a specified time limit is commonly used as anindication of viability of cells in culture. Both the control andtreated groups show a 70% attachment capacity within 1 hour ofculturing. This result in conjunction with cell morphology and countsupport the safety of gNO therapy for topical applications on mammalianskin tissue at least at a range between 100 to 200 ppm of gNO.

FIG. 18 shows the amount of migration of fibroblasts grown in a 3Dmatrix and exposed to 200 ppm NO for 8 hours per day for 3 days comparedwith control cells in air or conventional incubator. As seen from theseresults, NO does not appear to affect (or more specifically does notinterfere with) the migration of these fibroblasts under theseconditions.

FIG. 19 shows the amount of proliferation of fibroblasts grown in a 3Dmatrix and exposed to 200 ppm NO for 8 hours per day for 3 days comparedwith control cells in air or conventional incubator. Again, NO does notappear to interfere with the proliferation of fibroblasts under theseconditions.

FIG. 20 shows the tube formation in human endothelial cells grown inmatrigel and exposed to air (top panels) or 200 ppm NO (bottom panels)for 8 hours (left panels) or 24 hours (right panels). Again, nosignificant difference between exposure to air and 200 ppm can bediscerned.

Human Case Study

This case study involved a 55-year-old man with a 30 year history ofsevere venous disease, both deep and superficial, related to deep veinthrombophlebitis. Initially, while in his twenties, the patientdeveloped bilateral non-healing venous leg ulcers that were surgicallytreated. The surgical sites healed but the ulcers continued to recur.Initially, the patient presented with a small ulcer located just belowthe medial malleolus of the left ankle. Although not increasing in size,this ulcer did not completely heal with two years of standard of caretherapy.

Most of the time the wound base was covered with a biofilm—a tenacious,yellow-colored, gel-like material. Edema control was maintained by usinggraduated compression stockings. Antimicrobial dressings were triedincluding Manuka Honey, a starch iodine preparation (lodosorb, Smith &Nephew, Largo, Fla., USA), and colloidal silver (Aquacel AG, ConvaTec,Princeton, N.J., USA). His wound was frequently debrided in order tophysically remove the biofilm. This was generally ineffective as thebiofilm was frequently noted to be present again at the next visit.Twenty percent benzyol peroxide lotion was applied every few days inorder to trigger the development of granulation tissue; however, thiswas ineffective as well. At times there would be improvement as theulcer would appear to become covered with new skin only to break downweeks later. This poor progress to complete closure was noted despitewound care that addressed proper moisture balance, wound bedpreparation, and treatment of the underlying disease.

This failure of his wound to close had a significant impact on qualityof life for this patient. He made clinic office visits at least once amonth for the entire two years. The cost of the treatment, including thesurgeons time and treatment materials (several thousand dollars), putpressure on the health care system as well as on the patient, with himhaving to travel several hours each visit for treatment. As previoustreatments proved ineffective, the patient was invited to participate inthis experimental study. Following a discussion of the experimentaltherapy and potential risks, an informed consent was obtained.

The patient was seen at the clinic where the wound was assessed andphotographed (FIG. 22). The treatment regimen was explained and the useof the CidaNOx Delivery System and boot was demonstrated. Arrangementswere made to meet at the patient's home the following day to set up theequipment and for him to have a repeat training on the use of thetreatment system. Training included use of the system as well as safetyinformation on using the gas equipment.

Nitric oxide gas (ViaNOx-H, VIASYS Healthcare, Yorba Linda, Calif., USA)was applied to the lower extremity with use of a gas-diluting deliverysystem (CidaNOx Delivery System) designed specifically for the study(PulmoNOx Medical Inc., Edmonton, Alberta, Canada). This CidaNOxdelivery system contains an internal air pump for dilution of the gNOand a flow control circuit to dilute the 800 parts per million (ppm) inthe NO source cylinder down to the therapeutic level of 200 ppm. Thetotal flow from the system was 1.0 L/min and included one-quarter of aliter per minute (250 ml/min) flow of gNO. Several internal pressuresensors assure the dilution flow is operational and monitor the system.The flow of nitric oxide was limited to 250 ml/min by a mechanically setpressure regulator and a mechanical flowmeter that have no externalcontrols that could be changed by the patient. The concentration ofnitric oxide delivered was assured by measurement of the CidaNOx outputwith a calibrated nitric oxide analyzer (AeroNOx, Pulmonox Medical Inc.)that is approved for monitoring inhaled NO in human patients.

The 200 ppm gNO from the CidaNOx Delivery System flowed out to a singlepatient use plastic boot that covered the patient's lower extremity. Theboot had an inflatable cuff near the top that provided a low-pressureseal. A secondary air outlet from the CidaNOx unit managed the inflationof the cuff. The patient connected the pump outlet to the cuff connectoruntil it was inflated and then the connector was sealed closed with theprovided clamp. The gNO flow was then connected to the inlet connectornear the toe of the boot and the return line to the connector near thetop of the boot. The return line passed through the CidaNOx unit andthen out through a scavenger consisting of charcoal and potassiumpermanganate that absorbs the nitrogen oxides. The CidaNOx DeliverySystem had two toggle positions, one for delivery of gNO and the otherfor delivery of air only. At the end of the treatment period, thepatient switched the delivery flow to air only so as to clear the bootof remaining gNO before taking the boot off.

The patient was instructed to continue wearing supportive stockings andto use a hydrofiber dressing (Aquacel, Convatec) on the wound when notreceiving gNO treatment. During the gNO treatment, he removed thesupportive stocking and replaced the Aquacel dressing with a porous, lowadherence dressing (ETE, Molnlycke Health Care, Sweden), which hadpreviously been shown to allow the diffusion of gNO through it (data notshown).

To explore the potential for wound bed preparation and accelerated woundhealing from prolonged use, treatment regimen beyond three days waschosen and which was stopped at 14 days to evaluate the short-termeffects and explore the possibility that the short-term effects wouldimprove the longer-term outcome. The patient was encouraged to wear thegNO boot as often as possible during each 24-hour period. As the patientworked during the day, it was decided that it would be most practical towear the boot and receive the gNO treatments only while in bed at night.The patient recorded the date, time, and duration of each treatmentperiod on a data sheet, and any significant observations related to thewound, treatment, or equipment. The wound size (cm²) was measured usingdigital photography and densitometry technique (Scion Image −4.02, ScionCorp., Frederick Md., USA).

The patient self-administered the treatment for 14 consecutive nights.The nocturnal treatment duration varied from 6.5 to 9.75 hour pertreatment. The cumulative wound exposure to 200 ppm gNO during the 14treatment periods was 105.25 hour. The wound was assessed andphotographed on day 0 (FIG. 22A, pretreatment), day 3 (FIG. 22B,following accumulative 24 hour of gNO exposure), and day 14 (FIG. 22C).The wound was also assessed and photographed ten days following thecompletion of the 14-day treatment (FIG. 22D) and in the 6th and 26thweek following the completion of the treatment (FIGS. 22E and 22F,respectively).

During the active treatment period, the subject was assessed withrespect to the use of the CidaNOx system. The subject found the systemeasy to use in a fixed location, found the application of the bagcomfortable, and never reported any pain associated with its use. Hesuffered no bleeding episodes. FIG. 23A shows the initial presentationof the ulcer prior to use of the gNO. The wound base was covered by abiofilm and there was little healthy granulation tissue present andthere was no evidence of new skin growth from the edges. The wound wasmalodorous.

After 24 hours of NO exposure (3 days at 8 hours day), for the firsttime there was healthy granulation tissue noted in the ulcer base. Therewas also early evidence of new skin growth from the edges observed. Themalodorous odor was also absent. Concomitantly, there was less biofilmpresent (FIG. 22B). At 14 days of therapy (FIG. 22C) the ulcer clearlyhad diminished in size. By then it had almost completely epithelialized.Significant wound size reduction was observed as early as day 3 of gNOtreatment (p=0.014), with approximately 75% reduction in wound area bythe end of gNO therapy at day 14 (FIG. 23). The wound was furtherassessed 10 days after cessation of gNO treatment (FIG. 22D). There didnot appear to be any deterioration of the wound during this time,although the ulcer was judged to be incompletely healed. No significantdeterioration in wound size was observed compared to the last day of gNOtreatment (FIG. 23). Six weeks later the wound was judged to be about90% healed with no deterioration in wound size or epithelialization(FIG. 22E and FIG. 23). At 26 weeks post NO discontinuation, the ulcerwas noted to be completely healed and reepithelialized (FIG. 22F). Overthe entire post-treatment time, there were no changes to the dressingregimen and no other anti-microbials or antibiotics were used.

The average time for ulcers that result from venous stasis disease toheal under optimal care ranges from 12 to 16 weeks. Our patient, who hada nonresponsive ulcer for more than two years, exhibited a positiveresponse to a brief exposure to gaseous nitric oxide. His wounddecreased in size, a granular base was established, and the malodoroussmell was eradicated during this two-week period. Further studies andrandomized controlled trials will be able to answer whether a longerexposure or a different concentration, once the biofilm was eliminated,would have made a difference in the closure of the lesions.

While embodiments of the present invention have been shown anddescribed, various modifications may be made without departing from thescope of the invention. For example, the types of tissue that may havewounds to be treated using the methods described herein may include,without limitation, the skin, muscle, tendon, ligament, mucosa, bone,cartilage, cornea, and exposed internal organs. The tissue may bedamaged by surgical incisions, trauma (mechanical, chemical, viral,bacterial, or thermal in nature), or other endogenous pathologicalprocesses. The invention, therefore, should not be limited, except tothe following claims, and their equivalents.

1. A method to promote healing of a wound of a subject, the methodcomprising the steps of: providing a flow-controlled source of nitricoxide gas; exposing the wound to a high concentration of exogenousnitric oxide gas for a treatment period without inducing toxicity to thesubject or the healthy cells surrounding the wound; and exposing thewound to a decreased concentration of exogenous nitric oxide gas for asecond treatment period sufficient to increase the expression ofcollagen MRNA.
 2. The method of claim 1, further comprising the step ofmonitoring the concentrations of nitric oxide gas.
 3. The method ofclaim 2, wherein the decreased concentration of nitric oxide gas isabout 5 ppm.
 4. The method of claim 2, wherein the treatment period isabout 7 hours and the second treatment period is at least about 7 hours.5. The method of claim 1, further comprising the step of monitoring ofthe levels of collagenase produced by cells surrounding the wound. 6.The method of claim 1, further comprising the step of monitoring thelevels of collagen produced by cells surrounding the wound.
 7. Themethod of claim 1, further comprising the step of removing of excessexudate from the wound.
 8. The method of claim 1, wherein the highconcentration of nitric oxide gas is greater than about 200 ppm.
 9. Themethod of claim 8, wherein the high concentration of nitric oxide gas isabout 200 ppm to 400 ppm.
 10. The method of claim 1, wherein thetreatment period is at least about 7 hours.
 11. The method of claim 10,wherein the exposure to the high concentration of nitric oxide gas inthe first treatment period is continuous.
 12. A method of reducingscarring in a healing process of a wound, the method comprising thesteps of: providing a flow-controlled source of nitric oxide gas;exposing the wound to a high concentration of exogenous nitric oxide gasfor a treatment period without inducing toxicity to the subject or tohealthy cells surrounding the wound, exposing the wound to a decreasedconcentration of exogenous nitric oxide gas for a second treatmentperiod sufficient to increase the expression of collagen mRNA; andexposing the wound to a third concentration of exogenous nitric oxidegas for a third treatment period, wherein the third concentration isbetween the high concentration and the decreased concentration.
 13. Themethod of claim 12, wherein the high concentration ranges from about 200ppm to 400 ppm, the decreased concentration ranges from about 5 ppm to20 ppm, and the third concentration ranges from about 20 ppm to 200 ppm.14. The method of claim 12 wherein the first treatment period is atleast seven hours in a day, the second treatment period ranges from 5–12hours a day, and the third treatment period ranges from about 5–12 hoursa day.
 15. The method of claim 14 wherein the first treatment period,the second treatment period, and the third treatment period are repeatedfor multiple days.